Center for Relativistic Laser Science

ICORS 2018

Stimulated Raman scattering has been used in label-free Raman imaging studies of live cells[1,2]. Important attempts to develope super-resolution Raman imaging with intense Raman pump or decoherence beam have been made. However, the intense beams beyond weak stimulated Raman scattering limit could complicate spectral characteristics of Raman gain or loss signals. Here, the dependences of stimulated Raman loss (SRL) signal on Raman pump intensity and pump-probe delay time (Δt) are investigated through both experimental and simulation studies. We perform a numerical simulation for the coupled wave propagation to investigate the effect of cross-phase modulation (XPM) on the stimulated Raman scattering (SRS)[3]. Our simulation involving both vibrationally resonant SRS and non-resonant XPM effects in part accounts for the Δt-dependent peak shift and spectral broadening as well as the appearance of a gain signal at negative time delays (Δt<0). At the high pump intensity, it is found that the anti-symmetric XPM signal with respect to the time zero (Δt=0) cannot be selectively eliminated to produce pure SRS signal by time-integration over Δt because of the increased interference term of the SRS and XPM at the Raman-active frequency region. We believe that our results discussed here would be of use in developing a super-resolution coherent Raman imaging microscope in the near future.

ACKNOWLEDGMENTS

This work was supported by the IBS-R023-D1 for M.C., the Institute for Basic Science (PB2017044) and the Korea Basic Science Institute (D37617) for H.R. All the SRL measurements were performed by using the femtosecond Multi-dimensional Laser Spectroscopic System (FMLS) at the KBSI.

REFERENCES

[1] C. W. Freudiger, W. Min, B. G. Saar, S. Lu, G. R. Holtom, C. He, J. C. Tsai, J. X. Kang, X. S. Xie, Science, Label-Free Biomedical Imaging with High Sensitivity by Stimulated Raman Scattering Microscopy 2008; 322: 1857-1860.

[2] B. G. Saar, C. W. Freudiger, J. Reichman, C. M. Stanley, G. R. Holtom, X. S. Xie, Science, Video-rate molecular imaging in vivo with stimulated Raman scattering 2010; 330: 1368-1370.

[3] S. Yoon, D. W. McCamant, P. Kukura, R. A. Mathies, D. Zhang, S. Y. Lee, J. Chem. Phys., Dependence of line shapes in femtosecond broadband stimulated Raman spectroscopy on pump-probe time delay 2005; 22: 024505.